Solar convection and oscillations in magnetic regions

TL;DR

This study uses advanced 3D magnetohydrodynamics simulations to explore how magnetic fields influence solar convection and oscillations, revealing changes in granulation and explaining the acoustic halo phenomenon.

Contribution

It provides new insights into the effects of magnetic fields on solar convection and oscillation excitation through realistic numerical simulations.

Findings

Magnetic fields alter granulation structure significantly.

Oscillation power decreases with increasing magnetic field, matching observations.

Enhanced high-frequency acoustic emission is linked to magnetic field-induced turbulence changes.

Abstract

The goal of this research is to investigate how magnetic field affects the dynamics of granular convection and excitation of solar oscillations by means of realistic numerical simulations. We have used a 3D, compressible, non-linear radiative magnetohydrodynamics code developed at the NASA Ames Research Center. This code takes into account several physical phenomena: compressible fluid flow in a highly stratified medium, sub-grid scale turbulence models, radiative energy transfer between the fluid elements, and a real-gas equation of state. We have studied the influence of the magnetic field of various strength on the convective cells and on the excitation mechanisms of the acoustic oscillations by calculating spectral properties of the convective motions and oscillations. The results reveal substantial changes of the granulation structure with increased magnetic field, and a frequency-dependent reduction in the oscillation power in a good agreement with solar observations. These simulations suggest that the enhanced high-frequency acoustic emission at the boundaries of active region ("acoustic halo" phenomenon) is caused by the changes of the spatial-temporal spectrum of the turbulent convection in magnetic field, resulting in turbulent motions of smaller scales and higher frequencies than in quiet Sun regions.